The analysis of samples and the determination of the presence or concentration of chemical species contained therein is a common and important process in chemistry and biology. Particularly important is the analysis of biological fluids, such as blood, urine, or saliva, to determine the concentration of various constituents. Also of great importance is the measurement of the concentration of various chemical constituents embedded within biological materials, such as tissue. Chemical analysis of blood, urine, and other biological fluids is crucial to the diagnosis, management, treatment, and care of a wide variety of diseases and medical conditions. In the case of diabetes, monitoring of blood glucose levels several times a day is necessary to the efficient management of this disease in many patients. Analysis of various blood components is of importance in both the diagnosis and treatment of diseases of the circulatory system. For example, the level of various types of cholesterol in the blood has a strong correlation with the onset of heart disease. Urine analysis provides valuable information relating to kidney function and kidney disease. The concentration of alcohol in the blood is known to be related to a subject's physical response time and coordination and can provide information related to, for example, the individual's fitness to drive a motor vehicle.
Additionally, there are many instances where it is desirable to measure the local concentration of chemical constituents in tissue, either in-vivo or in-vitro. For example, in stroke victims it is important to monitor the degree of brain edema or the concentration of various metabolic chemical constituents in the brain that serve as indicators of brain function. Such indicators include fatty acid compounds, water, blood, lactates, and certain proteins and lipids. Other specific examples may include the monitoring of tissue oxygenation or tissue blood perfusion as a means to of gauging the metabolic function of a human or animal subject.
Moreover, in many applications, a "real-time" measurement of chemical concentration in biological fluids is important. Current invasive methods require that a sample of fluid be removed from a subject and then analyzed in one or more chemical tests. The tests can be expensive and require skilled technicians to remove and analyze the samples. Furthermore, the analysis of samples may have an undesirably long turn-around time. Additionally, the tests are usually made in centralized clinical laboratories with a resulting complexity of sample tracking and quality control. These circumstances create additional problems related to the potential change in the chemical composition of the fluid between extraction and analysis and, even more detrimentally, the possibility of a sample being confused with the samples of other patients.
It is also advantageous to analyze the chemical nature of sample materials without physically extracting a sample from the subject. For example, it is advantageous to examine the chemical makeup of human blood without taking a blood sample. In addition to time and cost considerations such invasive testing causes skin trauma, pain, and generates blood waste.
For all of the foregoing reasons methods of "non-invasive" testing have long been considered an attractive alternative to invasive testing. However, prior non-invasive testing methods have suffered from a number of practical drawbacks. The present invention is a method of analytical and quantitative testing for the presence of chemical species in a test sample. The method is non-invasive and has wide utility, being easily applicable to the non-invasive measurement of humans, animals, plants, or even packaged materials. Being highly versatile the method is broadly applicable to both in-vivo and in-vitro samples.